Microbial Dynamics during Cheese Production and Ripening: Physicochemical and Biological Factors

Microorganisms are an essential component of cheese, playing an important role during its manufacture and ripening. Cheese microbiota can be composed by starter cultures, group formed mainly by lactic acid bacteria (LAB) such as Lactococcus, Lactobacillus, Streptococcus, Leuconostoc and Enterococcus involved in acid production and flavor development during ripening; adjunct microbial cultures and secondary microorganisms, which play an important role during ripening. Cheese is a typical example of a mixed fermentation process in which desirable and undesirable bacteria, yeasts and molds interact and compete during initial steps and ripening process, leading to a complex product whose characteristics depends on the dynamics of all these microbial populations, which is influenced by intrinsic and extrinsic factors, such as temperature, pH, moisture, manufacture conditions, biological factors, among others. The main biological factors that influence the increase of one population in detriment of other microbial populations are: direct competition for substrate, production of inhibitory metabolites (such as acetic acid, acetaldehyde, ethanol, diacethyl), and the secretion of bacteriocins. The inhibitory compounds are products of bacterial metabolism, whereas bacteriocins are antimicrobial peptides or proteins produced by different groups of bacteria, including LABs. Several examples show that the direct addition of bacteriocins or bacteriocin producing starter cultures interfere in the proliferation of undesirable NSLAB and harmful bacterial populations during cheese processing and ripening. Thus, the characterization of new bacteriocins and the selection of starter cultures, as well as their combination with nonthermal physical treatments offer excellent opportunities for the control of undesirable microbial communities in fermented dairy products. _____________________________________________________________________________________________________________